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Norwegian stratified-random bottom trawl surveys are carried out under the assumption that a constant area is swept by the trawl during a standard haul to generate abundance indices. Results from measurements of trawl geometry during a trawl survey in the Svalbard area, showed that there was a consi...
| Main Authors: | , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.611.1437 http://journal.nafo.int/j09/godo.pdf |
| Summary: | Norwegian stratified-random bottom trawl surveys are carried out under the assumption that a constant area is swept by the trawl during a standard haul to generate abundance indices. Results from measurements of trawl geometry during a trawl survey in the Svalbard area, showed that there was a considerable depth dependency, and to a lesser extent, area/bottom stratum depen-dency of wingspread. Assuming that the swept area was linearly related to the wingspread, it was found that the currently applied method relatively underestimates the younger ages of cod (1-3 years) in the Svalbard area. The use of instruments for monitoring trawl geometry during all tows is one way to diminish variability in bottom trawl survey indices. |
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